A concrete mixer truck is a vehicle that carries fresh concrete in a mixer drum and transports the fresh concrete from a fresh concrete factory to a construction site. To prevent the fresh concrete in the concrete mixer truck from decreasing in quality and hardening, the mixer drum is rotated normally so that the fresh concrete is agitated by a plurality of spiral blades provided in the mixer drum. Further, the concrete mixer truck is configured such that the fresh concrete in the mixer drum can be discharged by rotating the mixer drum in reverse. When the concrete mixer truck arrives at a concrete pouring site, the mixer drum is rotated in reverse so that the fresh concrete is supplied to a pouring location.
In this type of concrete mixer truck, the mixer drum must be rotated constantly until the fresh concrete is discharged. An engine of the concrete mixer truck is typically used as a drive source for driving the mixer drum. More specifically, by transmitting power from the engine to a hydraulic pump via a PTO (Power Take Off) and driving the hydraulic motor using working oil discharged from the hydraulic pump, the mixer drum can be driven to rotate by the hydraulic motor.
In a mixer drum driving apparatus that drives a mixer drum using only power from an engine, as described above, an engine rotation speed must be increased when the mixer drum is to be rotated at high speed. When the engine rotation speed is increased, noise is generated from the engine, and an increase in fuel consumption occurs. Further, when fresh concrete is carried in the mixer drum, the mixer drum must be rotated constantly to prevent hardening and the like. Therefore, the engine of the concrete mixer truck cannot be stopped even when the truck is stationary while waiting its turn to discharge the fresh concrete at a pouring site. As a mixer drum driving apparatus for solving these problems, JP2007-278430A discloses a mixer drum driving apparatus that drives a mixer drum to rotate by driving an auxiliary hydraulic pump using a motor while a concrete mixer truck is stationary, instead of driving a hydraulic pump using an engine.
However, the mixer drum driving apparatus disclosed in JP2007-278430A exhibits the following problems.
In this mixer drum driving apparatus, while the concrete mixer truck is stationary, all mixer drum driving, i.e. driving for the purposes of agitating, introducing, and discharging fresh concrete, are executed via the motor. Therefore, a high output motor must be used, leading to an increase in the size of the motor and a power supply. When the motor, the power supply, and related components required to drive the motor increase in size, the concrete mixer truck increases in weight.
An object of the present invention is to provide a mixer drum driving apparatus in which a motor and a power supply can be reduced in size.
According to an aspect of the present invention, a mixer drum driving apparatus has a mixer drum carried on a frame of a concrete mixer truck to be free to rotate, a fluid pressure motor that drives the mixer drum to rotate, and a fluid pressure pump that is driven by power from an engine of the concrete mixer truck in order to supply a working fluid to the fluid pressure motor. The mixer drum driving apparatus includes an auxiliary fluid pressure pump that is provided independently of the fluid pressure pump and is capable of supplying the working fluid to the fluid pressure motor so as to cause the mixer drum to perform agitation rotation, a plurality of motors configured to drive the auxiliary fluid pressure pump to rotate, and a control unit that controls rotation of the mixer drum. When the engine is stopped during the agitation rotation of the mixer drum, the control unit drives the auxiliary fluid pressure pump to rotate by operating the plurality of motors selectively in accordance with a load of the mixer drum.
Embodiments and advantages of the present invention will be described in detail below with reference to the attached figures.